1. Field of the Invention
The present invention relates to a lifting apparatus for use, for example, in constructing buildings, repairing highways, painting and the like at elevated locations in order to load operators or materials on a bucket attached thereto, and particularly to an operation control mechanism of the lifting apparatus capable of controlling the drive of a chassis of the lifting apparatus forward or backward in the same direction as the bucket is directed irrespective of the positional relationship between a turntable and the chassis.
2. Prior Art
There has been employed a lifting apparatus capable of raising or lowering an elevator or a bucket for assembling, painting and repairing at elevated locations such as a highway or building construction, wherein the operator or the material is loaded on or unloaded from the bucket or the elevator.
The lifting apparatus of this type is classified as a boom-type, scissors-type, X-type and the like. It is common to any type of such lifting apparatus that a control apparatus is installed in the bucket for controlling a chassis of the lifting apparatus. The operator on the bucket operates the control apparatus provided inside the bucket so that the lifting apparatus can perform various operations whereby the bucket can be raised to the height required for the working.
There have been employed in many cases a lever-type or joystick type mechanism in which the lever is pushed or pulled for turning on or off the switch so that a three-directional valve is switched for supplying oil under pressure. The three-directional valve is controlled to control the supply of oil under pressure to each part of the lifting apparatus and the adjustment of the amount of oil under pressure.
The lifting apparatus of this kind has an advantage that scaffolds can be omitted which enhances the convenient workability but a disadvantage that the operator is liable to involve unexpected accident at the time of operating the lifting apparatus.
Particularly, in the typically used boom-type lifiting apparatus, the turntable mounted on the chassis can be turned horizontally 360.degree. relative to the chassis. In view of such mechanism, the operator is liable to be involved in an accident at the time of driving the chassis forward or backward.
For instance, if the turntable is directed forward relative to the chassis, the chassis can move forward by pushing a lever forward. However, the lever to be pushed in forward direction or pulled in backward direction can be controlled with keeping the relation between the chassis and the turntable or the bucket but without any relation between the pushing or pulling direction of the lever and the direction of the turntable or the bucket. That is, the direction where the driving lever pushed or pulled is not at all related with the chassis direction where the turntable or the bucket is turned. Accordingly, when the chassis is traveled forward or backward while the turntable is turned 180.degree. relative to the chassis, i.e. in the rearward direction of the chassis and hence opposite to the normal forward direction, the operator feels a reverse driving feeling, i.e. as if he drove the chassis backward. That is, if the lever is pushed, i.e. in the forward direction of the bucket, the chassis travels forward while the turntable is directed to the rear side of the chassis. That is, the operator feels as if he drove the chassis backward. Accordingly, the operator must operate in a feeling reversed to the ordinary driving feeling.
Furthermore, in such a case, i.e. at the state where the turntable is turned 180.degree., an accident is more liable to occur. For example, if a beam or other building approaches the back of the operator in this case, a collision or the like is liable to occur which can be very dangerous. That is, there is a case that the operator pushes the lever forward for driving the turntable and the chassis forward in the normal driving mode in the direction of the boom. However, if the turntable on the chassis is turned backward relative to the chassis, then the chassis travels forward (i.e., opposite the direction of the boom). As a result, there may occur an accident in that the operator may be caught in the space between the bucket and a beam or building.
To minimize the chance of an accident resulting in injury or death, it is preferable to indicate the position of the turntable relative to the chassis on an indication panel of the control apparatus. However, the operator frequently overlooks the indication on the panel during the operation and realizes the mistake of the operation only when involved in an accident.
Although the structure having the turntable capable of turning through a full horizontal rotation relative to the chassis is very convenient in working operations such as repairing and painting at elevated locations, it is very dangerous to drive the chassis forward while the turntable is directed to the rear of the chassis since the operator feels as if he is driving the chassis backward.